The strong dependence of the EPR linewidth of fusinite particles on oxygen is used to monitor oxygen contents in liquids and cells. The mechanism of oxygen line broadening is being investigated in these materials. Methods to refine fusinite by density gradient centrifugation have been studied, as are techniques to separate the particles by size. The size and chemical composition of fusinite extracts are studied in order to develop more effective and sensitive natural and synthetic carbonaceous oxygen sensor materials.